The dairy cows at Walford and North Shropshire College are housed for eight months a year and their dung is collected and pumped into a digester.

There it is converted into methane and used to power a generator. This produces enough energy to run the farm.

Adrian Joynt, farm manager at the college's new £2.7m environmentally friendly Harris Centre, said: "Everything that comes out of the back end of an animal goes in [the digester].

"And what we get out is 7,500 kilowatts - or £7,500 worth. We actually get enough energy to supply the farm's electricity for a year."

He added: "If you are going to put food in one end of the cow, we have to accept what comes out of the other.

As what comes out releases methane and pollutes water, the wider use of methane digesters in agricultural settings seem a nearly ideal way to deal with the climate impact of animal agriculture (with the truly ideal likely being less consumption of meat). ::BBC News